A method of gene therapy in a subject in need thereof, the method comprising administering to the subject a vector that comprises a transgene for expression in the subject and a mirtron for knocking down expression of a gene in the subject, wherein the mirtron is in the 5′UTR of the transgene. Also a vector comprising a transgene for expression from the vector and a mirtron for knocking down expression of a gene, wherein the mirtron is in the 5′UTR of the transgene and wherein the 5′UTR further comprises an exonic splice enhancer motif and/or wherein the mirtron is flanked in the 5′UTR by a fragment of the coding region of a reporter gene, and methods for preparing a vector.